Problem: Solve for $r$ : $-4 = r - 23$
Solution: Add $23$ to both sides: $ \begin{eqnarray} \\ \hphantom{-4 {+ 23}} &\hphantom{=}& \hphantom{r} \\ -4 &=& r - 23 \\ \\ {+23} && {+23} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ -4 {+ 23} &=& r \\ \end{eqnarray} $ Simplify. $ r = 19$